In many targeting and missile guidance systems, optical based seekers are used to acquire, track and engage a prospective target. In the course of using these optical systems, the system is often required to focus on an image that is residing in a set of received imagery thought to contain a target. In accomplishing this objective, imaging systems of the present day are becoming more and more automatic in their ability to focus and lock onto a target.
Many advanced imaging systems have some type of autofocus capability. One autofocus technique is to measure or estimate the range to a target and adjust the focus based on this measured or estimated data. Another technique is to monitor the temperature of the optical system and adjust the focus position and focus related information based on the temperature. Since most optical systems have a focus which shifts or drifts as a function of temperature, this athermalization (i.e., temperature based focusing) allows for normalizing the focus over a range of temperatures encountered in operational scenarios.
All of the aforementioned techniques are based on the user or system requiring the supply of additional information regarding the system and various assumptions that the system is performing as it should in accordance with these various assumptions and design constraints. The conventional techniques use athermalization and range estimation to set the focus of the optics using these “perfect estimates”, which are in reality not so perfect. Upon processing and compensating for these estimates, the conventional systems provide the operator with an offset from these perfect estimates to achieve better focus.
These conventional systems have several disadvantages associated with their practical application. One problem is that the factory calibrated athermalization may drift significantly and change over time from the original calibration setpoint that was established in the factory. Another problem is that range estimation for many of these systems is based on flat earth approximations, which do not adequately compensate for the earth's curvature. These range estimation systems also do not compensate well for rough terrain, such as that containing hills, mountains and other topographic barriers. Therefore, these flat earth approximations are not always valid and tend to introduce inaccuracies into the system which in turn adversely impact the accuracy of systems that rely on these techniques.
Therefore, it is desirable to have a method and system which does not suffer from these disadvantages. The present invention solves these problems by deriving a metric of focus based on a scene followed by a shift in focus to obtain optimal performance.